Plant for the production of web-like paper material

ABSTRACT

Herein described is a plant for the production of web-like paper material comprising a forming equipment, which dispenses a paper material slurry on a support canvas, and a desiccating equipment, which is designed to desiccate the paper material slurry to form the web-like paper material. The desiccating equipment comprises at least one first rotary perforated cylinder and at least one second rotary perforated cylinder, on whose surface the paper material slurry conveyed by the support canvas dynamically adheres, and a heating system, which is designed to generate and deliver hot process air to at least one of the first rotary perforated cylinder and the second rotary perforated cylinder. The first rotary perforated cylinder is a cylinder operating under relative pressure conditions, wherein the hot process air is blown from inside the first rotary perforated cylinder towards the web-like paper material conveyed by the support canvas. The second perforated cylinder is a cylinder operating under relative vacuum conditions, wherein the hot process air is suctioned, through the second rotary perforated cylinder, from web-like paper material conveyed by the support canvas. A recovery circuit is designed for the recovery of the hot process air suctioned from the second rotary perforated cylinder and to deliver such hot process air to the first rotary perforated cylinder.

This application claims priority of Italian Patent Application No.102021000003974 filed on Feb. 22, 2021.

Technical Field

The present invention generally relates to a plant for the production ofweb-like paper material and, in particular, a plant of the so-called TAD(acronym for “Through Air Drying”) type for the production ofhigh-quality tissue paper.

BACKGROUND

As known, in the paper production process in general, and in the tissuepaper production process in particular, a step for drying the productbeing processed by evaporation must be carried out in order to extractthe surplus water content thereof. The product to be desiccated, usuallyconsisting of a fibrous slurry based on cellulose and diluted withwater, is initially prepared in an appropriate forming equipment and itis therefore delivered to a subsequent drying and desiccating equipmentafter an intermediate pressing step. At the inlet of the drying anddesiccating equipment, the slurry which forms the paper sheet beingprocessed contains a low dry part content, which can be equal to about24%-28%. In other words, after the pressing step the slurry may stillcontain up to 75% and more of water. Therefore, the step for extractingunder vacuum is not capable of eliminating all the water from the fibresof the slurry, which must therefore be removed by evaporation.

The finished product, typically but not exclusively consisting of tissuepaper, requires a dry part content well higher than the values reportedabove, that is typically equal to about 94%-98%. Therefore, thereclearly arises the need to extract from the fibrous slurry, in thedrying step by evaporation, most of the residual water content thereof,in order to obtain a sufficiently dry continuous paper sheet. After thedrying and desiccation step by evaporation, the paper sheet is stored inreels in order to be subsequently processed (so-called “converting”step) and, lastly, packaged for shipment and final retail sale.

Among plants for the production of web-like paper material of the knowntype plants of the so-called TAD (acronym for “Through Air Drying”) areknown and particularly valued. The TAD technology uses a hot air jetwhich traverses the fibrous slurry before the latter is wound on aconventional yankee dryer. Basically, by transferring sensitive heat,the air allows the evaporation both of the water retained by the fibresof the paper material and of the water chemically bound to the fibre ofthe cellulose.

In the TAD process, the paper material fibrous slurry is supported andaccompanied by a continuous and mobile support belt, typicallyconsisting of a canvas, of the type resistant to temperatures up to200-250° C. The canvas, and therefore also the paper material fibrousslurry follows the rotary surface of a perforated cylinder which allowsthe exchange of hot air with the paper material fibrous slurry.

Therefore, the TAD technology allows to produce high-quality tissuepaper, given that it is a drying technology which imparts a very slightimpact mechanical action on the paper material fibrous slurry, avoidingthe strong action of the conventional suctioning presses and/or blindholes. The final result is a paper sheet with greater voluminosity,softness and absorption capacity with respect to the ones manufacturedwith the conventional technologies, allowing a lower specificconsumption of fibre.

TAD-type plants currently provide for two types of operation for thepaper material fibrous slurry drying equipment, substantially linked totwo corresponding types of perforated cylinder. As a matter of fact,this perforated cylinder can operate under relative pressure conditions(so-called “Vertiflow Type”), or under relative vacuum conditions(so-called “Inflow Type”). For each type of perforated cylinder, thewinding of the paper material fibrous slurry being dried may be carriedout on two or more cylinders.

For example, document U.S. Pat. No. 3,303,576 A discloses a plant forthe production of web-like paper material according to the preamble ofclaim 1, wherein the perforated drying cylinders operate under relativepressure conditions. A plant for the production of web-like papermaterial wherein the perforated drying cylinders operate under relativevacuum conditions is instead disclosed in document FR 2733522 A1.Further plants of the known type for the production of web-like papermaterial are disclosed in documents US 2003/019601 A1 and US 2018/073195A1.

TAD-type plants comprising perforated cylinders which operate underrelative pressure conditions (“Vertiflow Type”) reveal drawbacks interms of specific drying capacity, due to the difficulty in maintainingthe paper material fibrous slurry adhered onto the surface of eachcylinder by tensioning the canvas. On the contrary, TAD-type plantscomprising perforated cylinders which operate under relative pressureconditions have simpler structural features, given that these perforatedcylinders which operate under relative pressure conditions are subjectedto low mechanical stress.

TAD-type plants comprising perforated cylinders which operate underrelative vacuum conditions (“Inflow Type”) have a greater specificevaporating capacity, which however depends on the capacity of therecirculation fan with which these plants are provided. On the contrary,TAD-type plants comprising perforated cylinders which operate underrelative vacuum conditions require a more robust mechanical constructiongiven that under operating conditions each cylinder is subjected to veryhigh mechanical stresses.

Irrespective of the type of plant, each perforated cylinder is thenprovided with a respective extractor hood and with a process aircirculation circuit comprising one or more recirculation fans, one ormore air heating burners and one or more extraction fans for theextraction of hot and humid air (the so called “fume”). The extractionfan must eliminate the water vapour produced by the drying of the papermaterial fibrous slurry, besides eliminating the air infiltration comingfrom the machine room through the contact sealings. Considering theamount of infiltrated air, despite the extraction temperatures beingaround 100° C. or slightly higher, the heat loss that occurs issignificant in this case.

It should be observed that when using two or more perforated cylindersin a TAD-type plant the average specific evaporate of the paper materialfibrous slurry decreases significantly moving from the first to the lastcylinder. Furthermore, it should be observed that in TAD-type plantscomprising perforated cylinders which operate under relative pressureconditions (“Vertiflow Type”) the canvas—which supports the papermaterial fibrous slurry (wet-formed) being dried and which keeps thispaper material fibrous slurry adhered to each perforated desiccatorcylinder—is particularly mechanically stressed given that must supportthe thrust of the traversing air which—from the internal of theperforated cylinder—must pass through towards the external.

On the contrary, in TAD-type plants comprising perforated cylinderswhich operate under relative vacuum conditions (“Inflow Type”) thecanvas is subjected to low mechanical stress, while the perforatedcylinder is subjected to high mechanical stress, given that it mustsupport the entire thrust of the traversing air from the external towardthe internal of the perforated cylinder.

SUMMARY

Therefore, an object of the present invention is to provide a plant forthe production of web-like paper material, in particular a so-calledTAD-type plant, which is capable of overcoming the aforementioneddrawbacks of the prior art in an extremely simple, cost-effective andparticularly functional manner.

In detail, an object of the present invention is to provide a TAD-typeplant for the production of web-like paper material that is simpler tomanufacture with respect to similar TAD-type plants according to theprior art.

Another object of the present invention is to provide a TAD-type plantfor the production of web-like paper material that, despite beingsimpler to construct with is respect to similar TAD-type plantsaccording to the prior art, is capable of manufacturing a high-qualityweb-like paper material.

A further object of the present invention is to provide a TAD-type plantfor the production of web-like paper material that allows to save energywith respect to similar TAD-type plants according to the prior art.

These objects according to the present invention are achieved byproviding a plant for the production of web-like paper material asdescribed in claim 1. Further features of the invention are outlined bythe dependent claims, which are an integral part of the presentdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of a plant for the production web-like papermaterial according to the present invention will be more apparent fromfollowing exemplifying and non-limiting description, with reference tothe attached schematic drawings, wherein:

-   -   FIG. 1 is a schematic view of the main components of a plant for        the production of web-like paper material according to the        present invention;    -   FIG. 2 is a detailed schematic view of the desiccating equipment        of the plant for the production of web-like paper material of        FIG. 1;    -   FIG. 3 is a partial cross-sectional view of a first drying        device of the desiccating equipment of FIG. 2; and    -   FIG. 4 is a partial cross-sectional view of a second drying        device of the desiccating equipment of FIG. 2.

DETAILED DESCRIPTION

With reference to the figures, a preferred embodiment of the plant forthe production of web-like paper material according to the presentinvention is shown. The plant is indicated as a whole with referencenumeral 10. As shown in the schematic view of FIG. 1, the plant 10 firstand foremost comprises at least one continuous support belt 14, 16,which is movable through a plurality of rollers 18, 20.

The plant 10 further comprises at least one forming equipment 12 forforming the web-like paper material 200. This forming equipment 12 inturn comprises at least one device 22 for dispensing a paper materialslurry 100. The dispensing device 22 is designed to deposit—on thesupport belt 14, 16—the paper material slurry 100 which must besubsequently dried. The paper material slurry 100 may be of any knowntype at the state of the art and it may comprise cellulose fibres and/orany other material suitable for manufacturing the web-like papermaterial 200, which preferably but not exclusively consists of tissuepaper.

At least one desiccating equipment 24, which is designed to at leastpartially desiccate the paper material slurry 100 conveyed by thesupport belt 14, 16, in order to form the web-like paper material 200Ais provided for downstream of the forming equipment 12. In theembodiment of the plant 10 shown in the figures there are provided for afirst support belt 14, belonging to the forming equipment 12, and asecond support belt 16, belonging to the desiccating equipment 24. Theconfiguration of the support belt 14, 16 may in any case be modifieddepending on the needs, while maintaining the technical function ofsupporting and conveying the paper material slurry 100 first and thenthe web-like paper material 200 within the entire plant 10. Preferably,each support belt 14, 16 may consist of a fabric with plain weave, madeof a material resistant to temperatures up to 200-250° C.

The desiccating equipment 24 comprises at least one first device fordrying the paper material slurry 100, which consists of a first rotaryperforated cylinder 26 on whose surface the paper material slurry 100conveyed by the support belt 16 is dynamically adhered. In detail, thefirst rotary perforated cylinder 26 is a cylinder with a circular basewith predefined diameter D1.

The desiccating equipment 24 further comprises at least one seconddevice for drying the paper material slurry 100, which consists of asecond rotary perforated cylinder 28 on whose surface the paper materialslurry 100 conveyed by the support belt 16 is dynamically adhered. Alsothis second rotary perforated cylinder 28 is a cylinder with a circularbase with predefined diameter D2. This second rotary perforated cylinder28 is therefore arranged downstream of the first rotary perforatedcylinder 26.

The desiccating equipment 24 further comprises a heating system 30, 32,34, 36, 38, 40, which is designed to generate hot process air and todeliver such hot process air to at least one of such first rotaryperforated cylinder 26 and such second rotary perforated cylinder 28. Inparticular, the heating system may comprise, sequentially and withreference to the first rotary perforated cylinder 26, one or morecomburent air e fans 34, one or more process air heating burners 30 andone or more pumps 40 for supplying the heated process air to the firstrotary perforated cylinder 26. Similarly, with reference to the secondrotary perforated cylinder 28, the heating system may sequentiallycomprise one or more comburent air fans 36, one or more process airheating burners 32, one or more process air fans 38 to move the heatedprocess air and one or more extraction fans 54.

The desiccating equipment 24 may also comprise, in a per se knownmanner, a further rotary heating cylinder 52, also referred to as“yankee dryer”. This yankee dryer 52, on whose surface the papermaterial slurry 100 is dynamically adhered for the final desiccationthereof, is arranged downstream of the second rotary perforated cylinder28.

The first rotary perforated cylinder 26 is a cylinder operating underrelative pressure conditions (“Vertiflow Type”), so that the hot processair is blown from inside the first rotary perforated cylinder 26 towardsthe paper material slurry 100 conveyed by the support belt 16 and whichis at least partially wound on the surface of such first rotaryperforated cylinder 26. The second rotary perforated cylinder 28 isinstead a cylinder operating under relative vacuum conditions (“InflowType”), so that, through the second rotary perforated cylinder 28, thehot process air is suctioned from the paper material slurry 100 conveyedby the support belt 16 and which is at least partially wound on suchsecond rotary perforated cylinder 28.

Advantageously, the diameter D1 of the first rotary perforated cylinder26 is smaller or larger than the diameter D2 of the second rotaryperforated cylinder 28. Having low specific evaporation, the secondrotary perforated cylinder 28 may operate at high temperature (up to200° C. and above), making extraction fume available at a temperatureuseful for blowing on the first rotary perforated cylinder 26 in cascadefashion.

According to the invention, the desiccating equipment 24 is actuallyprovided with at least one recovery circuit 42 which is designed for therecovery of the hot process air (extraction fume) suctioned from thesecond rotary perforated cylinder 28 and to deliver such hot process airto the first rotary perforated cylinder 26. This allows the hot processair to be blown onto the paper material slurry 100 additionally to thehot process air generated directly by the components 30, 34, 40 of theheating system which are connected to the first rotary perforatedcylinder 26.

Based on a preferred but non-limiting configuration of the plant 10, theis diameter D1 of the first rotary perforated cylinder 26 may becomprised between about 2 m and about 2.2 m, which correspond to adiameter D1 of about 7 feet in the imperial units system. The diameterD2 of the second rotary perforated cylinder 28 may instead be comprisedbetween about 2 m and about 7.5 m, which correspond to preferreddiameters D2 from a minimum of 7 feet (equal to about 2.13 m) and above.

A first rotary perforated cylinder 26 with small diameter, approximatelyequal to about 7 feet, allows to operate with low tension on the canvasof the support belt 16, with low traversing air flow rate and with highspecific evaporation of the paper material slurry 100, as well as withair outflow at low temperature (typically equal to about 85-90° C.) andhigh count (typically equal to about 200-350 grams of vapour perkilogram of dry air). A second rotary perforated cylinder 28 with largediameter, approximately in the order of 24 feet, 18 feet or 14 feet,instead allows to extract—from the paper material slurry 100—air at hightemperature and with flow rate sufficient to entirely or partly meet theblowing demand of the first rotary perforated cylinder 26, thanks to therecovery circuit 42, creating an integral or almost integral cascade.The balancing of the blowing air flow rates, of the blowingtemperatures, of the extraction flow rates and of the count of theextractions respectively of the first rotary perforated cylinder 26 andof the second rotary perforated cylinder 28 is managed by means of acomputerised algorithm linked with the drying process.

Still based on a preferred but non-limiting configuration of the plant10, shown in FIG. 2, the heating system 30, 34, 40 is designed togenerate and deliver hot process air to said first rotary perforatedcylinder 26 from the bottom upwards (or vice versa), through at leastone first conveyor 44 arranged beneath such first rotary perforatedcylinder 26. Also the recovery circuit 42, which recovers the hotprocess air suctioned by the second rotary perforated cylinder 28, maybe designed to deliver such hot process air to the first rotaryperforated cylinder 26 from the bottom upwards, through the firstconveyor 44. The extraction of the hot process air from the first rotaryperforated cylinder 26 is instead carried out by means of at least oneextractor 46 arranged above such first rotary perforated cylinder 26.

In the preferred but non-limiting configuration of the plant 10, shownin FIG. 2, the heating system 32, 36, 38 is designed to generate anddeliver hot process air to the second rotary perforated cylinder 28still from the bottom upwards, through at is least one second conveyor48 arranged beneath such second rotary perforated cylinder 28. However,it cannot be ruled out that the hot process air in the second rotaryperforated cylinder 28 can be delivered differently, such as for examplefrom the top downwards, while the outflow of such hot process air fromthe second rotary perforated cylinder 28 may be carried out by a lateralhead thereof or by both.

Preferably, one or more energy recovery devices may be provided for onthe extraction circuit 50, arranged downstream of the extractor 46, toextract the hot process air from the first rotary perforated cylinder26. In addition, the hot process air extracted by the first rotaryperforated cylinder 26 may also be delivered to the forming equipment12, arranged upstream of the desiccating equipment 24, so as to be usedas air for heating the paper material slurry 100 by means of one or moredistribution devices.

Preferably, the blowing temperature range of the hot process air by thefirst rotary perforated cylinder 26 may be comprised between about 80°C. and about 250° C. The temperature range for suctioning the hotprocess air by the second rotary perforated cylinder 28 may instead becomprised between about 100° C. and about 230° C.

Still preferably, the blowing count value for the first rotaryperforated cylinder 26 may range from 100 grams of vapour per kilogramof dry air to 350 grams of vapour per kilogram of dry air. This valuemay instead range from 70 grams of vapour per kilogram of dry air to 200grams of vapour per kilogram of dry air for the second rotary perforatedcylinder 28.

As shown in FIG. 3, in the step of dynamic adherence of the support belt16 and of the paper material slurry 100 supported by it to the firstrotary perforated cylinder 26, the paper material slurry 100 adheres tothe surface of the first rotary perforated cylinder 26, while thesupport belt 16 is outside and wound to the paper material slurry 100.This configuration allows the paper material slurry 100 not to detachfrom the support belt 16 while the first rotary perforated cylinder 26is in blowing mode.

Vice versa, as shown in FIG. 4, in the step of dynamic adherence of thesupport belt 16 and of the paper material slurry 100 supported by it tothe second rotary perforated cylinder 28, the support belt 16 adheres tothe surface of the second rotary perforated cylinder 28, while the papermaterial slurry 100 is outside This configuration allows the papermaterial slurry 100 not to penetrate into the holes of the second rotaryperforated cylinder 28 while the latter is in suction mode.

In the desiccating equipment 24 of the plant 10 there may also beprovided for possibility of replacing the first rotary perforatedcylinder 26 with a capillary absorption special roller, which may offerperformance similar to or higher than that of such first rotaryperforated cylinder 26, but without using traversed air. In this case,the capillary absorption roller would operate parallel to the secondrotary perforated cylinder 28.

The heating system of the desiccating equipment 24 may be obtained bothby means of fuel powered burners 32, 34, as shown in FIG. 2 and by meansof heat exchange batteries (which use steam, diathermic oil or otherfluids). There may be provided for the possibility of also using, asheating fluid, exhaust gases of cogeneration devices (turbines orinternal combustion engines) added to the main flow.

Therefore, it has been observed that the plant for the production ofweb-like paper material according to the present invention attains theobjects outlined above, in particular obtaining the followingadvantages:

-   -   the first rotary perforated cylinder 26 (so-called “Vertiflow        Type”), which is more expensive to construct, still has a small        diameter, therefore reducing the costs;    -   having low specific evaporation, the second rotary perforated        cylinder 28 (so-called “Inflow Type”) operates at high        temperature (up to 200° C. and above), making extraction fume        available at a temperature useful for blowing on the first        rotary perforated cylinder 26 in cascade fashion;    -   the management of the drying cycle is controlled by means of a        PLC or DCS, so as to optimise the drying cycle in order to        optimise the quality of the paper produced and minimise specific        costs.

The plant for the production of web-like paper material of the presentinvention thus conceived is in any case susceptible to variousmodifications and variants, all falling within the same inventiveconcept; furthermore, all details can be replaced by technicallyequivalent elements. Basically, the materials used as well as the shapesand dimensions may vary according to the technical needs.

Therefore, the scope of protection the invention is defined by theattached claims.

1. Plant (10) for the production of web-like paper material (200), theplant (10) comprising: at least one continuous support belt (14, 16),which is movable through a plurality of rollers (18, 20); at least oneforming equipment (12) for forming said web-like paper material (200),the forming equipment (12) comprising at least one device (22) fordispensing a paper material slurry (100), which is designed to depositsaid paper material slurry (100) onto said at least one support belt(14, 16); at least one desiccating equipment (24), which is arrangeddownstream of said at least one forming equipment (12) and which isdesigned to at least partially dry said paper material slurry (100)conveyed by said at least one support belt (14, 16), so as to form saidweb-like paper material (200), the desiccating equipment (24)comprising: at least one first drying device consisting of a firstrotary perforated cylinder (26), on whose surface said paper materialslurry (100) conveyed by said at least one support belt (14, 16) adheresdynamically, said first rotary perforated cylinder (26) being a circularcylinder with predefined diameter (D1), at least one second dryingdevice consisting of a second rotary perforated cylinder (28), on whosesurface of said paper material slurry (100) conveyed by said at leastone support belt (14, 16) adheres dynamically, said second rotaryperforated cylinder (28) being a circular cylinder with predefineddiameter (D2) and being arranged downstream of said first rotaryperforated cylinder (26), and a heating system (30, 32, 34, 36, 38, 40),which is designed to generate hot process air and to deliver said hotprocess air to at least one of said first rotary perforated cylinder(26) and said second rotary perforated cylinder (28), wherein said firstrotary perforated cylinder (26) is a cylinder operating under relativepressure conditions, and wherein said hot process air is blown frominside said first rotary perforated cylinder (26) toward said papermaterial slurry (100) conveyed by said at least one support belt (14,16), the plant (10) being characterized in that said second rotaryperforated cylinder (28) is a cylinder operating under relative vacuumconditions, wherein said hot process air is suctioned, through saidsecond rotary perforated cylinder (28), from said paper material slurry(100) conveyed by said at least one support belt (14, 16), and in thatsaid desiccating equipment (24) comprises at least one recovery circuit(42), which is designed to recover the hot process air suctioned fromsaid second rotary perforated cylinder (28) and to deliver said hotprocess air to said first rotary perforated cylinder (26), so that saidhot process air can be blown on said paper material slurry (100)additionally to the hot process air generated directly by the components(30, 34, 40) of the heating system which are connected to said firstrotary perforated cylinder (26).
 2. Plant (10) according to claim 1,characterized in that the diameter (D1) of said first rotary perforatedcylinder (26) is smaller than or equal to the diameter (D2) of saidsecond rotary perforated cylinder (28).
 3. Plant (10) according to claim2, characterized in that the diameter (D1) of said first rotaryperforated cylinder (26) is comprised between about 2 m and about 2.2 m.4. Plant (10) according to claim 2, characterized in that the diameter(D2) of said second rotary perforated cylinder (28) is comprised betweenabout 2 m and about 7.5 m.
 5. Plant (10) according to claim 1,characterized in that said heating system (30, 34, 40) is designed togenerate and deliver hot process air to said first rotary perforatedcylinder (26) from the bottom upwards, through at least one firstconveyor (44) arranged below said first rotary perforated cylinder (26).6. Plant (10) according to claim 1, characterized in that said recoverycircuit (42), which recovers the hot process air suctioned by saidsecond rotary perforated cylinder (28), is designed to deliver said hotprocess air to said first rotary perforated cylinder (26) from thebottom upwards, through said first conveyor (44).
 7. Plant (10)according to claim 1, characterized in that said heating system (32, 36,38) is designed to generate and deliver hot process air to said secondrotary perforated cylinder (28) from the bottom upwards, through atleast one second conveyor (48) arranged below said second rotaryperforated cylinder (28).
 8. Plant (10) according to claim 1,characterized in that said support belt (14, 16) consists of a fabricwith plain weave, made of material resistant to temperatures up to200-250° C.
 9. Plant (10) according to claim 1, characterized in thatsaid first rotary perforated cylinder (26) is designed to blow said hotprocess air at a temperature comprised between about 80° C. and about250° C., while said second rotary perforated cylinder (28) is designedto suction said hot process air at a temperature comprised between about100° C. and about 230° C.